1. Field of the Invention
The present invention relates to a method and an apparatus of controlling a sound force for an electronic musical instrument, more particularly, to an improvement with which a sound source circuit can always normally generate tone signals on the basis of input data such as positions or pressures corresponding to musical tone parameters from a performance operation member, and to an electronic musical instrument using a so-called physically modelled sound source as a sound source for forming a tone waveform, more particularly, to an electronic musical instrument which has a wide dynamic range of a tone volume to be able to stably and easily generate tones from a very weak tone such as a pianissimo tone up to a very strong tone such as a fortissimo tone.
2. Prior Art
An electronic musical instrument which generates performance tones of a rubbed string instrument such as a violin or of a wind instrument such as a clarinet comprises, as a musical tone waveform signal generating means a physically modelled sound source for physically simulating a mechanical vibration system of the rubbed string instrument or an air vibration system of the wind instrument by an electrical circuit. In an electronic musical instrument of this type, pitch data of an ON key is inputted upon operation of a keyboard, and a musical tone control signal (musical tone parameter) corresponding to a bow pressure or a bow velocity of a bowing operation in the rubbed string instrument, or a breath pressure or an embouchure of a blowing operation in the wind instrument is inputted to a sound source by a performance operation member comprising, e.g., a slide volume, thereby generating and producing an electronic tone.
The physically modelled sound source has parameters in physical images, such as a bow pressure, a bow velocity, a breath pressure, an embouchure, and the like, and changes these parameters, thereby variously and naturally changing tone colors in accordance with a tone volume, the way of performance, a time elapsed from the beginning of tone generation, or the like as in acoustic instruments.
However, in a conventional electronic musical instrument in which a musical tone control signal based on an operation position or an operation pressure of a performance operation member is merely multiplied with a given coefficient regardless of a velocity or pressure region, and is directly inputted to a sound source, a tone cannot be generated or an irregular or abnormal tone such as an uncomfortable tone or a so-called falsetto tone is generated in a given operation region. Therefore, in the conventional electronic musical instrument having the physically modelled sound source, the performance operation member must be operated while avoiding generation of these irregular or abnormal tones, thus making a performance operation difficult.
The present inventors proposed a method of controlling a sound source for an electronic musical instrument which was characterized in that operation member data of a performance operation member corresponding to a musical tone parameter was corrected on the basis of tone generation region characteristics according to an instrument, and corrected data was inputted to a sound source circuit, and filed this method in U.S. Ser. No. 07/648,156. According to this method, a musical tone parameter can be corrected to data within a predetermined tone generation region such as a tone generation start region, a tone generation sustain region, or the like, and then, the corrected parameter can be inputted to a sound source. Thus, the sound source can normally generate tones regardless of an operation state of the operation member.
This prior application presents an embodiment wherein boundaries of a tone generation region are approximated by two straight lines, and a region between the two straight lines is set to coincide with a region which can be defined by a corrected data value. However, boundaries of some tone generation region patterns cannot be approximated by only two straight lines with sufficient precision depending on an algorithm of a physically modelled sound source.
For example, FIG. 18 shows the relationship among a breath pressure, an embouchure, and a sound pressure of a saxophone. As shown in FIG. 18, a tone generation region of the saxophone has a relatively complicated pattern. Therefore, it can be estimated that as a physically modelled saxophone sound source approximates an air vibration system of the saxophone better, the tone generation region pattern of the sound source approaches that shown in FIG. 18. For example, the tone generation region in the physically modelled saxophone sound source having an arrangement shown in FIG. 2 is as shown in FIG. 3.
It is impossible to approximate the boundaries of the tone generation region by only two straight lines with sufficient precision like in the embodiment of the prior application. If the tone generation region is approximated by only two straight lines, the approximating straight lines undesirably pass inside the boundaries of the tone generation region, as indicated by dotted lines a and b in FIG. 3, so that corrected data does not include values in a non-generation region and in an irregular tone region as much as possible. In this case, a musical tone control parameter (corrected data) cannot be sufficiently changed up to near the boundaries in the original tone generation region, and a variable range of a tone color is undesirably narrowed. For example, hatched portions B and C in FIG. 3 respectively correspond to a region of a soft tone color, and a region of a hard, strong tone, and a tone color is largely changed in these regions. However, since these regions are located almost outside the straight lines, data in these portions cannot be adopted as corrected data. More specifically, since most of regions where a tone color is largely changed are omitted, expression power is impaired.
In the embodiment of the prior application, as one of two different musical tone parameters, data from the operation member is directly used, and the other parameter is corrected to fall within a region obtained by approximating the tone generation region. For this reason, an actual performance cannot always match with musical tones.
Furthermore, parameters such as a bow velocity, a bow pressure, a breath pressure, an embouchure, and the like have upper and lower limit values which are used by the sound source to start or sustain tone generation. For example, when the parameter is equal to or smaller than a given value, it does not satisfy an oscillation condition of the model, and no tone is generated. On the other hand, when the parameter value is set beyond an oscillation limit, even if the value corresponds to the lower limit value of the oscillation limit, a tone volume of a generated tone is relatively large. Since the embodiment of the prior application does not take the lower limits of these parameters into consideration in the control, the dynamic range of a musical tone is narrowed, and a performance with weak tones such as pianissimo tones cannot be performed, or tones are intermittently generated if possible. When the upper limit value is exceeded, no tone is generated, or an uncomfortable irregular tone is generated.